For collectors and enthusiasts for all things old and unusual, the Internet has brought a fantastically wide world within fingertip reach. No longer are antiques the preserve of the knowledgeable or the extremely dedicated. So nowadays, if you fancy tracking down antique kerosene heaters, it is easy. Here is a suggestion of how to start.
Ebay etc. These are easy auction sites - often you need to keep an eye out for a while for what you are looking for, but almost everything eventually comes up. There are similar, smaller sites to look at as well. With all online auctions, like with real life auctions, be careful not to get carried away. Decide what you are prepared to pay beforehand and stick to your limit. There will always be another chance.
Search engines. Okay, not so original, but a surprising number of people do not use these things very well. The key for collectors is to put in detail. If nothing comes up, then work backwards, eliminating detail until you find some sites of interest. Sometimes a little patience is needed.
The great thing about kerosene portable heaters is that the technology is fairly simple - more than likely you will be able to get a usable antique, which is always nice.
Do remember that the older heaters will not have the safety features of new indoor kerosene heaters (which will cut out if knocked and are really safe and easy to light), and they will need to be well ventilated. Get a heating engineer who knows about kerosene heaters to look it over before you use it!